GPRS has been developed to communicate efficiently packets of data to and from mobile nodes using either a 2G (for example GSM) or 3G (for example UMTS) mobile radio network. GPRS provides support for a packet-orientated service, which attempts to optimise network and radio resources when communicating data packets such as for example internet data packets.
Generally, the GPRS network will be connected to another packet data telecommunications network, which may also be connected to further packet data telecommunications networks. The GPRS network includes a gateway support node (GGSN) which provides an interface between an external packet data communications network and nodes attached to the GPRS network and provides a plurality of bearers for communicating internet packets with the nodes.
The Internet Protocol as developed by the Internet Engineering Task Force (IETF) has become a preferred way of communicating packet data via telecommunications networks. Whilst version 4 of the Internet Protocol (Ipv4) has been standardised and has been deployed in many fixed networks, version 6 of the Internet Protocol is being developed in order to provide improved facilities. Amongst these improved facilities is a facility to communicate data packets to and from mobile nodes, which roam from a home network to a foreign network during an IP session [1]. Generally, following a process known as route optimisation which will be described shortly, a source and a destination address in the header of IP data packets being sent from and to a Mobile Node (MN) respectively will change as a result of the MN roaming to the foreign network.
The MN may be communicating IP data packets with a Correspondent Node (CN) which is attached to a GPRS network, then the GGSN of the GPRS network must be arranged to route the IP data packets via an appropriate bearer to the CN (which itself may be mobile). If the MN roams to a foreign network mid-session then the GGSN must be arranged to route the IP data packets to the CN (mobile user equipment) via the appropriate bearer. The appropriate bearer will have been set up by the GGSN when a session initiation was established at a time when the MN was attached to its home network. As such the parameters for the bearer will have been established with reference to a home address of the MN as the source address. However as explained above, the source address in the header of the IP data packets will be changed during the session from the home address of the MN, when attached to its home network, to a care-of-address after the MN roams to the foreign network.
It has previously been proposed in co-pending UK patent application numbers 0226289.7, 0222187.7, 0230336.0, 0222161.2 and 0230335.2 to provide a mobile node's home address in an extension header field in IPv6 known as the hop-by-hop field. As such the GGSN will be able to identify the appropriate bearer through which IP data packets can be routed to a correspondent node (CN) attached to the GPRS network, because the MN's home address provides the source address with respect to which the appropriate bearer was set up. However according to the Ipv6 standard, if the hop-by-hop field option is selected then every router along a communications path followed by the internet data packets from an MN to the CN is required to read the mobile's home address in the hop-by-hop field. This requirement could represent a reduction in performance of a network formed by the routers, as a result of the router reading the mobile's home address although this address may not be relevant to the router.